Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.47   6.207%   $121.5752   $121.58   $121.60   $121.60  
  Purchase #2 $36.74   4.276%   $38.311   $38.31   $38.30   $38.30  
  Purchase #3 $112.97   4.799%   $118.3914   $118.39   $118.40   $118.40  
  Purchase #4 $183.69   9.695%   $201.4987   $201.50   $201.50   $201.50  
  Purchase #5 $109.38   4.124%   $113.8908   $113.89   $113.90   $113.90  
  Purchase #6 $199.80   11.399%   $222.5752   $222.58   $222.60   $222.60  
  Purchase #7 $206.70   6.280%   $219.6808   $219.68   $219.70   $219.70  
  7 purchase totals = $963.75       $1,035.9231   $1,035.93   $1,036.00   $1,036.00